1. Field of the Invention
The present invention relates to a variable valve lift apparatus. More particularly, the present invention relates to a variable valve lift apparatus which can change a valve lift with one cam.
2. Description of Related Art
In general, an internal combustion engine generates power by burning fuel and air received in a combustion chamber. In this case, when the air is to be drawn, an intake valve is put into action by driving a camshaft, to draw the air into the combustion chamber while the intake valve is opened. And, when the air is to be exhausted, an exhaust valve is put into action by driving the camshaft, to exhaust the air from the combustion chamber while the exhaust valve is opened.
In the meantime, optimum operation of the intake valve or the exhaust valve varies with an engine rotation speed. That is, an appropriate lift of a valve opening/closing timing is controlled according to the engine rotation speed. Thus, in order to embody an appropriate valve operation according to the engine rotation speed, a variable valve lift (VVL) apparatus is under research, for embodying the valve to operate at a lift varied with the engine rotation speed. As an example of the variable valve lift apparatus, there is a device having a plurality of cams provided to a cam shaft for driving a valve with lifts different from one another for selecting a cam to drive the valve according to a situation.
However, if the plurality of cams are provided to the cam shaft, a configuration of making selective change of the plurality of cams for operating the intake valve or the exhaust valve can become complicated and interferences among the elements in the configuration are bound to take place. If the plurality of cams are operated independently for preventing the interferences among the configuration elements from taking place, leading to requiring an element for operating each of the cams, a cost is liable to increase.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.